1. Field of the Invention
This invention relates to a mixture of polycyclic aromatic polycarboxylic anhydrides carrying nuclear nitro groups that is substantially soluble in acetone but substantially insoluble in water and a process for preparing the mixture by treating a carbonaceous material with nitric acid and dehydrating the resulting product.
2. Description of the Prior Art
Aromatic anhydrides, such as benzophenone-3,4,3',4'-tetracarboxylic dianhydride and pyromellitic anhydride, are useful compounds as curing agents, for example, in combination with epoxy resins. These materials, however, are costly and it would be desirable to prepare aromatic anhydrides that would similarly be useful as curing agents but that would be inexpensive.